This invention relates generally to an electrophotographic printing machine, and more particularly concerns an apparatus for controlling dispensing and mixing of marking particles into a developer unit.
In a typical electrophotographic printing process, a photoconductive member is sensitized by charging its surface to a substantially uniform potential. The charged portion of the photoconductive member is exposed to a light image of an original document being reproduced. Exposure of the charged photoconductive member selectively dissipates the charge in the irradiated areas to record an electrostatic latent image on the photoconductive member. After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer material into contact therewith. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules to the latent image forming a toner powder image on the photoconductive member. The toner powder image is then transferred from the photoconductive member to a copy sheet. The toner particles are heated to permanently affix the powder image to the copy sheet.
In most two component development processes, the developer/toner materials are at the mercy of the development housing design: auger configuration, sump geometry, magnetic brush roll size, magnetics design, roll and auger velocity, etc. to cause tribocharging of the toner against the carrier. The auger speeds and roll velocities are usually adjusted to the adequate flow balancing of the developer within the housing and developability that provides ample operating latitude, respectively.
Once these speeds are determined, the level of tribocharging of the toner against the carrier is fixed. Hence, to modify the tribocharging, the formulation of the materials are adjusted to provide the desired tribocharging performance. In conventional two-component xerographic development, the ability of a toner material to charge with a given carrier material is quantified as follows: At=Tribo*(TC+C0) where Tribo is the average charge to mass ratio of toner, TC is the toner concentration in percent by weight, and C0 is a constant. At is a critical specification parameter for toner and developer; it tends to vary from batch to batch, with developer age, and with operating relative humidity. The variation with humidity is a special problem with many color toners, since this variation tends to be much larger than with comparable black toners. In general, the higher the At, the better the material charging. Modification of the developer At by changing the material""s formulation is a long process whereby the materials must be subjected to a significant amount of both bench and lengthy, and expensive full process experiments before they can be qualified for satisfactory use in a product.
A problem associated with the above system is in accommodating print jobs having wide area coverage requirements or low area coverage requirements. When the document has high area coverage, charging of the fresh toner is reduced due higher toner throughput in the housing which results to increased toner emission from the housing. When the document has low toner coverage, excessive mixing occurs; toner is impacted into the carrier thereby resulting to reduce material life.
An objective to the present invention is to alleviate the above problems and still maintain the adequate flow balancing of the developer within the housing and have developability that provides ample operating latitude.
In accordance with one aspect of the present invention, there is provided an electrophotographic printing machine having a latent image is recorded on a photoconductive member with the latent image being developed with marking particles by a developer unit, includes: a sump for storing a supply of marking particles; a dispenser for discharging marking particles from said sump into the developer unit; an auger for mixing marking particles in the sump to be transport to a donor member at a predefined mixing rate; an image processor for processing image information of the latent image to be recorded; means for generating a first output signal corresponding to the average area of the image information of the latent image to be recorded; means for recording a test patch; means for developing the test patch with marking particles; means for measuring a density of the test patch; means for generating a second output signal corresponding to the density of the test patch; means, responsive to the first and second output signals, for generating a control signal that is transmitted to said dispenser to regulate dispensing rate of marking particles into the sump; means for generating a third output signal corresponding to the dispensing rate of marking particles into the sump; and means, responsive to the first control signal and dispensing rate, for variably adjusting the predefined mixing rate of the marking particles in the sump, said variably adjusting mean having means, responsive to charging rate, for dynamically tuning said variably adjusting means. Pursuant to another aspect of the features of the present invention, there is provided a method for controlling dispensing and mixing of marking particles to develop a plurality of print jobs to improve material life and performance of the marking particles, the method comprising the steps of: predicting the quantity of marking particles required to reproduce each print job in said plurality of prints jobs; dispensing marking particles to maintain a predefine level in said sump; printing a first print job from said plurality of print jobs; mixing marking particles at a first mixing rate response to the quantity of marking particles required to reproduce said first print job; printing a second print job from said plurality of print jobs; mixing marking particles at a second mixing rate response to the quantity of marking particles required to reproduce said second print job.